NATIONAL JOURNAL OF MEDICAL RESEARCH print ISSN: 2249 4995│eISSN: 2277 8810 NJMR│Volume 10│Issue 3│July –Sept 2020 Page 141 Original Article Frequency of Subgroups of Blood Group “A” and “AB” amongst the Blood Donors in a Regional Cancer Institute of North East India and its Importance: A Retrospective Study Chandana Kalita, Anupam Sharma, Jagannath Dev Sharma, Amal Chandra Kataki, Manoj Kalita Authors’ affiliations: Medical Officer, Blood Bank; Professor, Dept. of Pathology; Director, Dept. of Gynec.; Statisti- cian, PBCR, Dr. B Borooah Cancer Institute, Guwahati Correspondence: Dr. Anupam Sharma, Email: dranupamsarma@gmail.com, Mob. No.: 8876595307 ABSTRACT Introduction: ABO Blood group system was discovered by Karl Landsteiner in the year 1900 who classified the blood groups into A,B,AB and O on the basis of the presence or absence of the antigens A and B on the cell surface of Red blood cells.Further ,in the year 1911, Von Dungern and Hirszfeld divided the group A into A1 and A2 hence total of six blood groups A1,A2,B,A1B,A2B,O. Aim of the study is to find out the frequen- cy of subgroups of A and AB Blood groups and its importance in transfusion practice. Methods: A total of 5594 blood donors’ samples were collected in a one-year period who came to donate blood. Blood grouping was done by the conventional tube method both forward and reverse grouping. Sub grouping of A and AB was done by using the commercially available Lectin Anti A1 (Tulip diagnostics, Goa ,India) .Group A red blood cells which agglutinate with Anti A1 lectin are classified as subgroup A1,whereas which do not agglutinate are classified as A2. Result: Out of total 5594 blood donors, 1354 belonged to group A and 413 constituted group AB. The per- centage of A1 amongst the A blood group is 93.94% (1272) and A2 is 6.056 (82). The percentage of A1 amongst the AB blood group is 91.04% (376) and A2 is 8.95% (37) Conclusion: The frequency of A1 subgroup is more in comparison to A2 in both A and AB blood groups amongst the blood donors. Identification and recording of subgroups is important in blood bank in respect to blood group discrepancy, blood transfusion reactions as well as Organ transplantation. Key words: blood group, subgroup A1, A2, Transfusion reaction INTRODUCTION: ABO Blood group system was discovered by Karl Landsteiner in the year 1900 who is considered as the father of transfusion medicine. The ABO antigens are defined by carbohydrate moieties on the extracel- lular surface of the red blood cell (RBC) membranes. They are also highly expressed on the surface of a variety of human cells and tissues, including epitheli- um, sensory neurons, platelets, and vascular endothe- lium. The ABO and Rh blood group system remain the most important blood group systems. 2,3 The fre- quency of ABO blood groups varies greatly in differ- ent races and populations. The prevalence of blood group O is highest in most of the population fol- lowed by B, A and AB. 4 A and AB have been divided into subgroups A1, A2, A1B and A2B depending on the reaction with anti A1 Lectin ,the extract from the seed of lectin Dolichos biflorus or human anti A1 se- rum.Anti A1 agglutinates A1 and A1B cells but not A2 and A2Bcells.Subgroups weaker than A2 occur infrequently. They are characterized by the declining number of A antigen sites on red cells and reciprocal increase in H reactivity. Weaker variants of A are A3, Ax, Am and A Intermediate. Anti A1 reacting at 220C or lower has no clinical significance but if re- acts at 370C is significant resulting in the blood group discrepancy, incompatibility and transfusion reaction. 1,5 MATERIALS AND METHODS A total number of 5594 blood samples were collect- ed from the blood donors who came to blood bank as replacement or voluntary donors for a period of two years from January to December 2016-2017 with their due consent according to the NBTC guidelines following the donor questionnaire. Ethical clearance for the study was obtained from the Institutional Ethical Committee. The identity and the gender of the donors was not revealed in any manner in the study conducted. Blood grouping was done by the conventional tube method. Both the forward and re-